The dependence of BTI and HCI-induced frequency degradation on interconnect length and its circuit level implications

The dependence of bias temperature instability (BTI) and hot carrier injection (HCI)-induced frequency degradation on interconnect length has been examined for the first time. Experimental data from 65-nm test chips show that frequency degradation due to BTI decreases monotonically for longer wires because of the shorter effective stress time, while the HCI-induced component has a nonmonotonic relationship with interconnect length due to the combined effect of increased effective stress time and decreased effective stress voltage. Simple aging models are proposed to capture the unique BTI and HCI behavior in global interconnect drivers. A closed-loop simulation methodology that takes into consideration the interplay between the frequency degradation and the stress parameters (such as stress duration and stress voltage) is used to determine the optimal repeater count and sizing in practical interconnect circuits.